Conventional IP techniques consist of asking questions of a subject and recording verbal and physiological responses. Psychophysiological measurements employed in the detection of deception have typically included skin conductance or skin resistance, continuously monitored blood pressure (and, since each heartbeat results in changes in blood pressure, heart rate), and breathing as measured by expansion of the chest. No psychophysiological measure has ever been found to actually measure deception. Rather, certain physiological response patterns have been held to be indicative of particular emotional responses that are likely to accompany deception in a well-orchestrated interrogation situation.
The questions asked of the subject in conventional IP techniques fall into four categories: Relevant questions, Irrelevant questions, Control questions, and Concealed Information questions. Relevant questions are questions directly related to the focus of an investigation. Irrelevant questions are irrelevant to the investigation and are structured so as to have little or no emotional significance for the subject. They are used for the purpose of comparison. Responses to these questions establish the typical response of the subject to questions about which he is not concerned.
Control questions are questions that are not directly relevant to the situation under investigation, but are designed to elicit an emotional response from the subject that is similar to the response elicited by the Relevant questions from a guilty subject. They are often general questions about types of undesirable behavior in which the subject may have been involved in the past, and are designed to elicit concern and/or doubt in the subject about the veracity of his response, or perhaps to stimulate the subject to lie. They, too, are used for the purpose of comparison: they establish the typical physiological response of a subject to questions about which the subject is concerned.
Concealed Information questions focus on information about the crime or situation under investigation that would be known only to the guilty party. It is hypothesized that a guilty individual will respond more to (that is, be more physiologically aroused by) correct details about the crime than to incorrect details, but that innocent subjects will respond the same to either.
These four types of questions are employed in three different techniques of questioning, the Relevant/Irrelevant (R/I) technique, the Control Question technique (CQT), and the Concealed Information technique.
The original "lie detection" technique was the Relevant/Irrelevant technique. In the R/I technique, two types of questions are presented: Relevant and Irrelevant. It is presumed that an innocent person will respond the same to the two types of questions because the person is unconcerned about the crime, whereas a guilty person will be more aroused by the Relevant questions, because the person is more concerned about the crime.
This technique has some serious drawbacks, the most obvious of which is that the Relevant questions concern subject matter that is inherently more upsetting than the Irrelevant questions. Therefore a large response to the Relevant questions may be the result of the emotional tendencies and physiological lability of the subject, rather than of deception. Moreover, in the cases where the subject does not respond at all to the Relevant questions, there is no indication that the subject would have responded had the questions been about the subject's criminal activity. In short, there is no control, and as a result both false negatives and false positives occur. Because of this, the R/I technique is seldom used in investigations of a specific crime or situation, although it is still used in nonspecific investigations such as pre-employment and personnel screening.
The most frequently employed technique in the investigation of specific crimes or situations is the Control Question Technique, which was developed to deal with some of the problems of the R/I technique. In the CQT, subjects are asked not only Relevant and Irrelevant questions, but also Control questions designed to elicit an emotional response. It is hypothesized that an innocent subject will respond more to the Control questions, since the subject is not concerned about the crime at hand, whereas a guilty person will respond more to the Relevant questions, since the person is more concerned with the crime than with a general question about something undesirable he may have done in the past.
Concealed information techniques are of two kinds: the Guilty Knowledge test and the Peak of Tension test. Both work on the premise that a guilty person will exhibit a larger physiological response to correct details about the crime under investigation than to similar details that do not fit the crime, whereas an innocent person will respond the same to both.
In the Guilty Knowledge test, subjects are asked a variety of questions about details of the crime that would be known only to the guilty party. Unlike the other techniques mentioned, this test can employ multiple-choice questions as well as "yes or no" questions. It is hypothesized that a guilty person will respond differentially to the correct, crime-relevant details.
In the Peak of Tension test, a question concerning a relevant and correct detail about a crime is embedded in a series of parallel questions mentioning similar but incorrect details. The sequence of questions is known in advance to the subject. It is hypothesized that the physiological response will peak at the time of the relevant question.
While the aforementioned tests are presumed to measure physical responses to provocative/innocent questions, it is known that such tests are subject to countermeasures by a determined, knowledgeable and trained subject. Moreover, it is known that the stimuli for all of the physical responses measured by the detection apparatus arise in the brain. While the art of measuring electrical signals emanating from the brain (scalp) is well developed, no effort, to the inventors' knowledge, has been made to use those measurements in IP, to discover whether subjects have or do not have concealed information or information regarding the subject of an investigation.
It is known that information obtained by recording Event-Related Brain Potentials (ERP's) can be used as a tool in the study of cognitive functions. These psychophysiological data augment the data that can be obtained by the traditional methods of psychology, which rely on the measurements of overt performance or on subjective reports. Such data are obtained by placing electrodes on a person's head and recording electroencephalograph (EEG) activity while the person is engaged in a task. Using the technique of signal averaging, information can be extracted from the EEG in the form of an ERP that is time-locked to some event of interest. One component of the human ERP is the P300 signal which was first reported by Sutton et al. "Evoked-Potential Correlates of Stimulus Uncertainty" Science, 1965, 150, 1187-1188.
Since this initial report, the P300 has been observed in a wide variety of difference circumstances. This invention makes use of the P300, a positive-going component of the ERP with a modal latency of about 300 msec. (time measured from stimulus to peak of the P300 component). An extensive body of research has shown that the P300 component of the ERP can be used to distinguish reliably between stimuli that are comparatively infrequent (rare) and/or contain meaningful information for an individual, as compared to stimuli that are comparatively more frequent and/or do not contain relevant information. The paradigm used for this purpose is known as the "Oddball" paradigm. In this paradigm a Bernoulli series of events is presented to the subject (i.e. on any given trial, one of two stimuli can occur, and their probability is complementary). If attention is paid to the entire series and one (or perhaps two) of the classes of events or stimuli in the sequence (the "oddballs") appear with a lower probability, then events in the rare class or classes will elicit a larger P300. If these comparatively rare stimuli contain information that is relevant, meaningful, or noteworthy for the subject, then the P300 component elicited by these stimuli will be larger still.
The P300 response occurs as soon as the subject has recognized and categorized the stimulus, after only about 300 milliseconds. There is no evidence in the published literature that the P300 component can be suppressed as long as the subject recognizes the stimuli and knows to which category it belongs. Behavioral manipulations of the type used as counter-measures in conventional detection of deception methods (e.g. tightening muscles to elevate blood pressure) can begin only after stimuli have been recognized and categorized--and the resulting P300 elicited. These P300's can be detected with excellent reliability by using readily available EEG equipment.
It is an object of the present invention to utilize a subject's EEG signals in IP.
It is a further object of this invention to provide an IP system based upon monitoring and processing of a subject's P300 components.
It is a further object of this invention to provide an EEG based interrogative polygraphy system which manifests high accuracy.